Insect Science (2013) 20, 228–234, DOI 10.1111/j.1744-7917.2011.01495.x
ORIGINAL ARTICLE Pollinating fig wasp Ceratosolen solmsi adjusts the offspring sex ratio to other foundresses
Hao-Yuan Hu1, Zhong-Zheng Chen1, Zi-Feng Jiang2, Da-Wei Huang3,4, Li-Ming Niu5 and Yue-Guan Fu5 1Key Laboratory of Biotic Environment and Ecological Safety in Anhui Province, College of Life Sciences, Anhui Normal University, Wuhu, Anhui Province, China, 2Department of Biology, University of Maryland, College Park, Maryland, USA, 3Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing, China, 4Plant Protection College, Shandong Agricultural University, Tai’an, Shandong Province, China, 5Environment and Plant Protection Institute, Chinese Academy of Tropical Agricultural Sciences, Danzhou, Hainan Province, China
Abstract Local mate competition theory predicts that offspring sex ratio in pollinating fig wasps is female-biased when there is only one foundress, and increased foundress density results in increased offspring sex ratio. Information of other foundresses and clutch size have been suggested to be the main proximate explanations for sex ratio adjustment under local mate competition. Our focus was to show the mechanism of sex ratio adjustment in a pollinating fig wasp, Ceratosolen solmsi Mayr, an obligate pollinator of the functionally dioecious fig, Ficus hispida Linn., with controlled experiments in the field. First, we obtained offspring from one pollinator and offspring at different oviposition sequences, and found that offspring sex ratio decreased with clutch size, and pollinators produced most of their male offspring at the start of bouts, followed by mostly females. Second, we found that offspring sex ratio increased with foundress density, and pollinators did adjust their offspring sex ratio to other females in the oviposition patches. We suggest that when oviposition sites are not limited, pollinators will mainly adjust their offspring sex ratio to other foundresses independent of clutch size changes, whereas adjusting clutch size may be used to adjust sex ratio when oviposition sites are limited. Key words behavior, co-evolution, local mate competition, mutualism, pollinating fig wasp, sex ratio adjustment
Introduction highly structured population, such as mating only between full siblings, evolutionary stable strategy models predict a Sex ratio in a local environment has been taken as a model female-biased sex ratio (Hamilton, 1967; Maynard Smith, of sex ratio theory (Hamilton, 1967; Frank, 1985; Herre, 1976). In haplodiploid hymenoptera, with haploid males 1985, 1987; West et al., 2000; Steiner & Ruther, 2009; (developed from unfertilized eggs) and diploid females West, 2009) and a case study of adaptation in evolution- (developed from fertilized eggs), the primary sex ratio is ary biology (Fellowes et al., 1999). In a random-mating determined by the mothers’ control of fertilization at the populations of infinite size, natural selection favors equal time of oviposition (Charnov, 1982). investment in both sexes, and an equal sex ratio is an There may be natural selection on foundresses to adjust evolutionary stable result (Fisher, 1930). However, in a their offspring sex ratio because of local mate competition (LMC) (Charnov, 1982; West et al., 2005). When patches are founded by one female and all mating occurs between Correspondence: Hao-Yuan Hu, College of Life Sciences, siblings, brothers may compete locally with each other Anhui Normal University, Wuhu, Anhui Province 241000, for mating with their sisters. Such LMC selects for fewer China. email: [email protected] male offspring (Sheldon & West, 2002). If offspring in a